How to Analyze Relative Density Data and Write a Conclusion
Research: The data being analyzed below is about relative density and buoyancy.
Relative density is a comparison of densities.
Buoyancy refers to something floating in a fluid (gas or liquid).
In the diagram, the Box-shaped boats are all floating in water. This means that each boat is buoyant in water. Notice that the water line (which is the surface) touches the sides of boats A, B, and C at the same place. Thus these boats have the same density. Lets pretend that each boat’s density is
0.4 grams/1 mL. The true density of water is 1 gram/1 mL. Relative density is the comparison of the density of two substances.
Relative Density = Density of the boat ÷ Density of water
= 0.4 grams/1 mL ÷ 1 gram/1 mL
= 0.4
When the relative density is less than 1, the object will float (it is buoyant).
Boats A, B, and C all have the same relative density as compared to water. Thus they are all equally buoyant.
Look at the second group of boats, D, E, and F. Notice that the boats are not equally buoyant.
Notice that the boats are the same size. But each of the boats have a different mass, thus they have different densities.
Density for boat D = 0.4 grams/1mL
Density for boat E = 0.5 grams/1mL
Density for boat F = 0.6 grams/1mL.
The Relative Density for each boat compared to water would be:
Boat D = 0.4 grams/1mL ÷ 1.0 grams/1mL= 0.4
Boat E = 0.5 grams/1mL ÷ 1.0 grams/1mL = 0.5
Boat F= 0.6 grams/1mL ÷ 1.0 grams/1mL = 0.6
Analysis of Data
The greater the density of the boat, the greater is the boat’s relative density as compared to water.
The greater the relative density of a boat compared to water the less buoyant is the boat and the lower the boats sinks in the water.
Lets Investigate
The following information in red type is experimental data from a 6th grade student. I added the Question:
Question: What effect does the mass of a boat have on the mass of cargo the boat can hold?
Student Project Hypothesis: If the mass of a boat increases, then the of cargo the boat can carry decreases.
Student Questions about Data Analysis
I did this with aluminum boats with increasing mass. My data show that as the mass of the boat increases, I need more pennies to sink the boat. I thought it would need less pennies. Is my data wrong or is my hypothesis wrong?
Thoughts from Janice
Your information is a bit sketchy. I assume that you built three boats from aluminum foil, each boat with a different mass. With the boats floating in water, you added pennies to represent the mass of cargo. You counted the pennies each boat could hold before it sank.
I assume that you increased the mass of the boats by using different amounts of aluminum foil. From your results, I assume that you did not make each boat the same size. Thus, you changed two variables, the mass of the boats and the size of the boats.
An experiment should test the effect of one variable on another variable. A variable is something that can change.
In your investigation, you changed the mass of the boats. This is called an independent variable.
The aim of your investigation is to decide how the mass of the boats effect the mass of the cargo the boats can hold without sinking.
The mass of the cargo depends on the mass of the boat. Thus, the mass of the cargo is called the dependent variable.
Results: A chart showing the mass of each boat with the number of pennies each could hold just before sinking.
Analyze Data
From your results, you would state that as the mass of the boats increased the mass of the cargo the boat could hold increased.
How to Write a Conclusion:
When Data Doesn’t Support the Hypothesis
If your data doesn’t support your hypothesis,
DO NOT assume that your hypothesis is wrong.
Your conclusion for the data you collected could be something like this:
Example Conclusion:
Three aluminum boats with different masses were made. Each boat was placed in a container of water. Pennies were counted as they were added to each boat. The last penny that caused each boat to sink was not counted. The results for the three tests did not support my hypothesis, which was that as the mass of a boat increases, the mass of the cargo it can hold and still float would be decrease.
I expected the more massive boat to hold fewer pennies, instead the more massive boat held the most pennies.
Since I did more than one test, I think that my data was correct. But for future investigations, I will do more than three tests.
Even though the experimental data did not support my hypothesis, and I did multiple tests, I still think my hypothesis is correct. Thus, my conclusion for this investigation is that while the data did not support my hypothesis, I am not at this time reporting that the hypothesis is incorrect. Instead, I will check my experiment to make sure that it properly tested my hypothesis. More investigations are needed.
If you have time, analyze the testing method.
Think About This:
1. The experiment should only test one variable, the mass of the boats. All other variables, including the size of the boat should stay the same.
2. From your results, I am guessing that the boats were not the same size.
Density is the measurement of the mass divided by the volume of the boat. If all the boats had been the same size, they would have had the same volume. Thus, the more massive boats would have had a greater density, a greater relative density as compared to water, and been less buoyant. The less buoyant a boat is the lower it sinks in the water.
I hope this helps.
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Science Standards
Some of the standards are the same for grades K-12. It it up to the teacher to figure out how to adapt them to their specific grade levels. This is where you can really help by providing specific ideas.
Scientific Investigation and Reasoning Skills
K-4: All students should develop abilities necessary to do scientific inquiry.
Analyze and interpret information to build reasonable explanations from direct (observable) and/or indirect (inferred) evidence.
5-8: All students should develop abilities necessary to do and understand scientific inquiry.
Analyze and interpret information to build reasonable explanations from direct (observable) and/or indirect (inferred) evidence.
9-12: All students should develop abilities necessary to do and understand scientific inquiry.
Analyze and interpret information to build reasonable explanations from direct (observable) and/or indirect (inferred) evidence.
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Matter
K-4 Develop an understanding of properties of objects and materials.
Classify matter based on physical properties, including mass, volume, relative density, physical state (solid, liquid, and gas; fluid).
5-8 Develop an understanding of properties and changes of properties in matter. (mass, volume, relative density, density)
Classify matter based on physical properties, including mass, volume, buoyancy (sinking, floating), relative density, density, physical state (solid, liquid, and gas; fluid).
9-12 Develop an understanding of structure and properties of matter.
Classify matter based on physical properties, including mass, volume, buoyancy (sinking, floating), relative density, density, physical state (solid, liquid, and gas; fluid).
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Note: Engineers use science information to design and construct boats and ships.
